MODELING OF OPTOELECTRONIC PROCESSES IN SrS:Cu ACTFEL DISPLAY DEVICES
This study explores the optoelectronic processes in SrS:Cu electroluminescent devices. It focuses on the reflective electrode dielectric stack, underlying mechanisms causing electron behavior, and the resulting luminance characteristics. Key insights include a hypothesized mechanism for luminance linked to electric field changes and the role of ionized activators in electron recapture. Despite advances, the model shows limitations, highlighting the need for further research to fully understand electron dynamics and device performance.
MODELING OF OPTOELECTRONIC PROCESSES IN SrS:Cu ACTFEL DISPLAY DEVICES
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MODELING OF OPTOELECTRONIC PROCESSES IN SrS:Cu ACTFEL DISPLAY DEVICES V.P. Singh University of Kentucky, Lexington Ky A. Garcia The University of Texas at El Paso, El Paso Tx A. Aguilera Hewlett Packard, Ft. Collins Co D.C. Morton U.S. Army Research Laboratory Adelphi, Maryland
REFLECTIVE ELECTRODE DIELECTRIC STACK Va PHOSPHOR 1µm DIELECTRIC STACK TRANSPARENT CONDUCTOR GLASS SUBSTRATE Typical VIL for ZnS:Mn Display Device Device Structure
Mn e- 3 5 2 Electrode 4 1 Electrode Insulator Phosphor Insulator 1) Electron ejection due to high electric field from the cathodic interface 2) Electron gains velocity, becoming “hot” 3) Electron impact excites activator atom (Mn or Cu) 4) Impacting electron reaches anode contributing to the built-in reverse field 5) Excited atom relaxes, emitting light
Comparisons • Secondary Luminance Peaks • Total Luminance is Small • Comparable Amount of Tunnel Current
Possible Causes for Low Luminance • Lack of Tunnel Current (not the case) • Excessive Impact Ionization - but this can Only Explain low Luminance but does not Explain Secondary Peaks • “Other” Mechanism Needed to Explain Behavior
Hypothesize We Hypothesize a Mechanism that Causes Luminance with a Field Reduction for a Given Device History
During dent ramp iL(t) 0, however there is an increase in L(t) means that electrons are recaptured by ionized activators a) Come from Interface State and only Recaptured by nearby Ionized Activators b) Formed by the Activator and a Defect Produced by the Activators Presence in the Lattice electrically forming a Dipole
Dipoles Positively Charged Activator Negatively Charged Trap • Are Activator-Bulk Trap pair Formed by the Introduction of the Activator in the Phosphor • Bulk Trap is Localized in Close Vicinity of the Activator • A Certain Minimum Field is Needed to Create/Maintain the dipole
Transient Results Tunnel Current appears in the very first pulse Luminance becomes noticeable in the 4th voltage pulse
Conclusions • A more Complete Model is required to study SrS:Cu • Currently this Dipole Model is able to Explain the Observed Features but • Further work is required
